DE 10 2005 017 802 describes a glow plug having a combustion chamber pressure sensor in which a ceramic heating element designed as a sheathed-element glow plug is situated in a housing. The ceramic heating element is surrounded by a supporting tube, which is secured by a seal in the housing. The seal is formed by a graphite ring situated between the supporting tube and the housing.
The mechanical stresses induced by the cyclic thermal stress in actual engine operation impair the adhesion to the interface between the metallic supporting tube and the ceramic heating element, which results in failure of the sealing function due to partial or complete loss of mechanical contact at the interface between the metal and the ceramic.